5 years later, are maxout networks dead, and why?
Basically, if you read the full paper (especially, the abstract and the section 7), you find that the main accomplishment remains a marginal contribution on top of dropout.  

If you see the empirical results on Table 5 (of the page 5) of the maxout's original paper, you find that the misclassification rate is only very, very slightly lower than that of dropouts. (2.47 % instead of 2.78%)

That could explain the relatively lower interest in the work.